Process and test kit for cocaine detection

ABSTRACT

Test kit and method for discriminating cocaine and its salts from substances that falsely give a positive color reaction with Scott&#39;s thiocyanate reagent. As all Scott false positive substances have lower pKa values than cocaine, or in their basic from higher pKa values than the cocaine base, they can be discriminated from cocaine by a suitable pH test of the solution. The pH indicator is preferably organic or lipophilic so that it can be dissolved in a solvent immiscible with water. The partitioning of the organic cocaine base or its salt between an organic and water phase of specific pH is used to further distinguish the test substance.

FIELD OF THE INVENTION

The present invention relates to a process and test kit for detectionand identification of cocaine, more specifically, cocaine and "crack",which do not give false positive results with other substances.

BACKGROUND OF THE INVENTION

As illicitly manufactured drugs are marketed and transferred from handto hand without any manufacturer's identification and specification andas it is not possible to distinguish visually sugar, salt, heroin,crack, and cocaine, it is necessary to examine the presumptive drugsubstances in a laboratory. The crime laboratories, however, are oftenvery busy so that such drug tests may take too long to keep the suspectsmeanwhile in custody. Many police agencies have therefore turned to testthe presumptive drugs themselves. Thus, chemical spot test kits havebeen commercially developed which shall allow an easy identification ofnarcotics and drugs of abuse. Many law enforcement agencies are usingthese kits as the investigator can now easily check the suspected drugsubstances within minutes. Conventional test kits for detection andidentification of cocaine are commonly based on contacting the suspectedsubstance with a cobalt thiocyanate solution. The formation of arelatively water insoluble turquoise complex indicates the presence ofcocaine or its salts. As the cobalt thiocyanate test is relativelysimple, it is also in use outside the laboratories. Notwithstanding,there is a great demand for a more specific test kit.

The standard Scott test is based on a colour reaction with cobaltthiocyanate (L. J. SCOTT (1973), Specific Field Test For Cocaine,Microgram, VI, 179). The corresponding commerical test kit contains thenecessary chemicals in three prefilled hermetically sealed glass ampulesor tubes and comprises the following steps:

Step A. The first tube contains cobalt thiocyanate in a solution of 1:1water and glycerine which forms a characteristic blue precipitate withsalts of cocaine.

When the cobalt thiocyanate is dissolved in water alone, a blueprecipitate is formed with nearly every alkaloid substance. The additionof glycerine (1:1) to the aqueous reagent, however, reduces thesolubility of most drug substances other than cocaine to almost zero, sothat these other substances cannot participate in a falsely positivecolour reaction. By this way, it is possible to exclude drugs such asheroin, methadone, quinine etc. However, cocaine stays soluble in such amixture of water and glycerine and can give a good response.

Crack, which is a cocaine base, reacts with Scott's reagent slower andwith less colour intensity. The addition of acid, however, convertscrack to its salt and enhances its colour reaction.

L. J. Scott reports that four drugs in this stage will react with thesame colour reaction as cocaine: (1) phencyclidine (PCP); (2) dibucaine;(3) butacaine; (4) methapyrilene. The two steps below shall excludethese four drugs:

Step B. By adding concentrated hydrochloric acid, the initially bluesolution is converted into a clear pink solution.

Step C. By adding chloroform the blue complexed cocaine is partitionedinto the organic phase.

The Scott test has several disadvantages. L. J. Scott himself reportsthat (i) the ratio of solution A to B is critical. When an excessiveamount of hydrochloric acid (solution B) is added to solution A, afterthe colour reaction with cocaine, a blue rather than a pink solution isformed, and the blue will no longer be extractable into the chloroformlayer after the addition of solution C. (ii) On the other hand, when anexcessive amount of cocaine is present in step A, it can be sometimesnecessary to add two additional drops of hydrochloric acid which makesthe test prone to errors. (iii) Furthermore, Scott has only tested alimited number of drugs. Since then, it has been found that also someother compounds can give a blue colour with Scott's reagent, e.g.dixyrazine.

With the cobalt thiocyanate reagent of ODV Inc., which is hereaftercalled "Scott's modified reagent", procaine, tetracaine and methadonegive a colour reaction similar to cocaine. Thus, this single reagentcannot really serve as a specific colour reagent for the identificationof cocaine, since false positive results are also obtained withsubstances that have similar response characteristics.

The European Patent No. 0 233 063 discloses a process and kit for thepresumptive identification of cocaine or heroine street drugs. Thisprocess comprises applying to the sample to be tested a reagent,comprising a sulfonated aromatic pH indicator which gives acharacteristic colour reaction in the presence of trace amounts oforganic bases or acetic acid. The process provides a quick test for thedetection of street drugs which can then, for example, be followed bythe Scott's test. In order to deal with the increasing number of similarstreet drugs, i.e. in their base form, it has become necessary tocombine several tests to exclude false positive results.

The deficiencies of these tests have led the inventor to develop anotherspecific reagent, which is intended to be used in combination withScott's reagent or Scott's modified reagent, in order to screen outfalse positive results in the Scott reaction. This other specificreagent allows surprisingly an error-free positive identification ofcocaine and its salts.

SUMMARY OF THE INVENTION

In accordance with the invention there is provided a process for thedifferentiation of cocaine and/or its salts from other substances thatmay react with Scott's cobalt thiocyanate reagent or Scott's modifiedreagent similar as cocaine and its salts. This is accomplished byapplying to a sample of the suspected drug a reagent which gives acharacteristic colour reaction in the presence of trace amounts ofcocaine and its salts and another colour reaction with false positivesubstances.

The present invention also provides a kit for cocaine detectioncomprising:

a) Scott's cobalt thiocyanate reagent or Scott's modified reagent;

b) a pH indicator solution which has a distinctive colour in thepresence of cocaine and another, different colour in case of a substancegiving a false positive result with Scott's reagent or Scott's modifiedreagent wherein the indicator is dissolved in a solvent immiscible withwater; and

c) a buffer solution of pH 7 for partitioning the organic base to theorganic phase.

DETAILED DESCRIPTION OF THE INVENTION

Contrary to the prior art approach for the detection of cocaine and itssalts, it has been found that cocaine and its salts, i.e. cocaine andcrack, in a powder can be differentiated by its basic character fromsubstances that give with cobalt thiocyanate a false positive colourreaction.

Cocaine belongs to a class of natural products known as alkaloids; thisterm is used to designate nitrogen-containing compounds of vegetableorigin which commonly have a heterocyclic ring system and one or morebasic nitrogen atoms. The basicity is a fundamental property of thesesubstances which all have at least one nitrogen atom; it is affected bythe aromatic and aliphatic character and by the substituents. Electronreleasing substituents like CH₃ increase and electron withdrawingsubstituents like COOH or COOR decrease the basicity.

Cocaine is a very weak base. It comprises a tropane structure and anitrogen carrying three alkyl substituents. Nevertheless, the basiccharacter of this nitrogen is very weak, probably, because of acombination of steric factors and its two esters which are electronwithdrawing substituents. The pKa of cocaine is 5.6.

All substance that give false positive results with Scott's reagent orthe Scott's modified reagent have a much stronger basic character,except for lidocain which is less basic than cocaine. In particular:

(A) PCP comprises a piperidine ring which has strong basic character.Piperidine has a pKa of 11.1, and 1-ethyl piperidine, which is a betteranalog to PCP, has a pKa of 10.45.

(B) Dibucaine is a strong base because of its triethylamine group.Triethylamine has a pKa of 11.01.

(C) Butacaine is also a strong base. It has a dibutylpropylamine groupwhich has a pKa similar to dibucaine.

(D) Methapyrilene is a strong base because it has a trimethylaminegroup. Trimethylamine has a pKa of 9.81.

(E) Dixyrazine is a strong base because of its piperazine group.Piperazine has a pKa of 9.83.

(F) Lidocaine is a very weak base because of its acetamido group.

The following substances also produce false positive reactions withScott's modified reagent:

(A) Procaine has a triethylamine group as dibucaine.

(B) Methadone is a strong base and it has dimethylpropylamine group witha pKa greater than 10.

(C) Tetracaine is a strong base as well. It has dimethylamine groupwhose pKa is 10.73.

The method according to the invention is preferably carried out with anorganic and/or lipophilic pH indicator reagent which produces adistinctive colour reaction in the presence of trace amounts of cocaine.The indicator does not react or give another colour reaction withsubstances that have a different (higher or lower) basicity thancocaine, and which react with Scott's reagent or Scott's modifiedreagent.

Preferably, the lipophilic pH indicator is selected from phthaleinindicators such as tetrabromophenolphthalein ethyl ester andnaphtholphthalein.

The colour reaction of the lipophilic pH indicator is preferably done intwo steps:

First, a small amount of the indicator is dissolved in a solventimmiscible with water, for example in chloroform, dichloromethane or1,2-dichloroethane. A trace amount of the suspected cocaine is thenplaced in a test tube, and a few drops of the indicator solution added.The solution is observed because a free organic base will cause a changein colour in dependence of the characteristics of the indicator and thebasicity of the base.

Second, when there is no change in colour, a few drops of an aqueousbuffer of pH 7 are added and the solution is observed once again. If asalt of an organic base is present, the organic base will be partitionedto the organic phase and react with the indicator, which can beobserved.

EXAMPLE 1

About 25 mg of tetrabromophenolphthalein ethyl ester (TBP) is dissolvedin 100 ml dichloromethane, giving a yellow solution. A trace amount ofthe suspected cocaine is added to a small test tube, after a part of thesubstance has been tested positive with Scott's reagent or Scott'smodified reagent. Even a substance that has been reacted with Scott'sreagent may be used. A few drops of TBP reagent are added to the testtube. An immediate intensive green colour confirms the presence of"crack" (cocaine base).

If there was no change in colour, a few drops of the aqueous buffer pH 7are added. If the suspected substance is a cocaine salt, a green colourinstantly appears in the lower phase (dichloromethan phase).

Reacting the indicator solution with a larger amount (a few milligrams)of cocaine gave a more intensive green colour reaction.

Substances reacting falsely positive with Scott's reagent gave in thismethod the following colour reactions:

Trace amounts (<1 mg) of PCP, dibucaine, methapyrilene, butacaine,dixyrazine, tetracaine, procaine and methadone gave a red colour. With alarger amount, a purple colour was observed. Lidocain gave no change ofcolour or, if at all, a very faint yellow-brown colour.

The above-identified indicators behave in this example as follows:

First, when using a high concentration of the indicator (50 mg/100 mldichloromethan) a red colour reaction like for Scott false positivesubstances is observed, even when a few milligrams of cocaine arepresent. However, trace amounts of cocaine (<1 mg) give a green colour.All false positive substances give a red or purple colour reaction.

On the other hand, when using a low concentration of the indicator (5mg/100 ml dicloromethan) and a few milligrams of cocaine in the reactionmixture, the colour reaction is blue, whereas all the false positivesubstances give a red or purple colour reaction, except for lidocainewhich gives no or a very faint, easily distinguishable yellow-browncolour.

When trace amounts of cocaine (<1 mg) are present, a green colour isobserved whereas under the same conditions the false positive substancesgive a red or purple colour reaction. It is essential therefore, to usea proper concentration of the indicator and to have a sample with onlytrace amounts of the cocaine.

Second, when a basic buffer is used, the same results can be observed inthe chloroform layer but the buffer solution is blue.

Third, when an acidic buffer is used, no colour reaction is observedwith cocaine.

EXAMPLE 2

Naphtholphthalein was used as the indicator. 25 mg of the indicator wasdissolved in 50 ml of chloroform. The solution had no colour. Theprocedure was similar as above. Results: With "crack" and cocaine thechloroform solution remained colourless. All the other drugs mentionedabove gave a yellow chloroform solution. The results can be commented asfollows: First, the indicator is less sensitive than TBP and, second, byusing a basic buffer the indicator is extracted into the buffer layer.

What is claimed is:
 1. A process for discriminating cocaine and/or itssalts from substances that give a false positive result in a Scott testcomprising the following steps:a) reacting a substance with a cobaltthiocyanate reagent or Scott's thiocyanate reagent; b) applying to asubstance that gives a positive result in step a) a solution containinga phthalein pH indicator, wherein(1) when said substance is a cocainebase the solution turns a cocaine-indicative color or does not changecolor, or (2) when said substance is a substance giving a false positiveresult with Scott's test reagents the solution turns a color which isdistinguishable from said cocaine-indicative color; and c) adding a fewdrops of an aqueous buffer solution of pH 7, if there has been no changein the color of the indicator solution of step b), wherein(1) whencocaine salts are present the resulting solution appears saidcocaine-indicative color, or (2) when substances giving false positiveresults with Scott's test reagents are present, the resulting solutionis a color distinguishable from said cocaine indicative-color.
 2. Theprocess according to claim 1, wherein the phthalein indicator islipophilic or organic or both.
 3. The process according to claim 1,wherein the phthalein indicator is tetrabromophenolphthalein ethylesteror naphtholphthalein.
 4. The process according to claim 1, wherein thecolor reaction of the phthalein indicator is done in two steps:a)dissolving a small amount of the phthalein indicator in a solventimmiscible with water and adding a few drops of said indicator solutionto the test substance so there is a change in color of the solution whenan organic free base is present; and b) adding a few drops of aqueousbuffer of pH 7 if there is no change in the color of the solution instep a), and when there is a salt of an organic base, the organic baseis partitioned into the organic phase to produce a solution that iseither said cocaine-indicative color or a color distinguishable fromsaid cocaine-indicative color.
 5. The process according to claim 4,wherein the solvent immiscible in water is chloroform, dichloromethaneor 1,2-dichloroethane.
 6. The process according to claim 1 for testingtrace amounts of cocaine and/or its salts in the range of less than 1mg.
 7. The process according to claim 1 for discriminating cocaineand/or its salts from phencyclidine, dibucaine, butacaine,methapyrilene, dixyrazine and lidocaine.
 8. The process according toclaim 1 for discriminating cocaine and/or its salts from procaine,tetracaine and methadone.
 9. A kit for detection and identification ofcocaine and/or its salts and for use in a process according to claim 1,comprising:a) a cobalt thiocyanate reagent or Scott's thiocyanatereagent; b) a pH indicator solution wherein the indicator is dissolvedin a solvent immiscible with water and wherein said solution turns saidcocaine-indicative color or does not change color in the presence ofcocaine or turns a color distinguishable from said cocaine-indicativecolor in the presence of substances giving a false positive result inScott's test; and c) an aqueous buffer of pH 7 for transferring anorganic base to the organic phase.